frying bacon noise in ch #1 of 1959 (with sound sample)

Discussion in 'The Workbench' started by grainman, Aug 1, 2019.

  1. grainman

    grainman Active Member

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    i have a white noise in the bright ch of my 1959 , it sound like fryin bacon , managed to tame it with a noise gate in the efx loop but im fed up now, like to find the main cause of it. it started after i blew a power tube i think, can it be a bad cap or resistor making this frying bacon noise ...anyone has a clue? i already try to pin point the trouble with some of you guys but without results
     
  2. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    If a gate in the loop helps it probably aint nothing to do with power tubes or power stage.

    Does it appear by itself or with guitar playing (signal)?
    If by itself pull V1. Anything change?
    If no change then pull V2. Anything change?

    This can be figured out.
     
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  3. Gene Ballzz

    Gene Ballzz Well-Known Member

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    ^^^^^ What he said, on all counts! ^^^^^
    Just Sayin'
    Gene
     
  4. fifteenohms

    fifteenohms Well-Known Member

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    Change the ketchup-drop capacitors for watermelon.

    I take Patreon youre welcome
     
  5. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    No. Use oranges and dates. Send me your funds. :)
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    What have you done so far to locate the noise?
    Did you swap out the preamp tubes one at a time with a new one?
     
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  7. john hammond

    john hammond Active Member

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    1. do what ampmad just said, swap/replace preamp tubes one at a time.
    2. chopstick test, to me it sounds like cracked resistor, take amp out of shell, turn upside down, turn it all on and tap each resistor ( and solder joint ) see if it makes a cracking sound.
    3. re-heat each solder joint, can't hurt.
    4. take knobs off and make sure pots are screwed in tight, sometimes they don't ground there because of oxidising over time. You can take pots off, scrub right where pots touch chassis with metho and plastic pot scourer, put pots back on. This is just good maintenance too.
     
  8. Neal

    Neal New Member

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    It's usually the 100K Carbon Composition plate resistors that are the culprit. Replace them all with new CC's, Carbon Film or Metal Film resistors of the same value.
     
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  9. grainman

    grainman Active Member

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    yes i did change all the tubes and when v1 is unplugged the noise stops.....also when i have my noise gate in the efx loop it works...so its tellin me even if im not an expert in the domain that it can be in the bright ch around v1...maybe the 2x 68k at the input i suspect what do you guys think of it ?
     
  10. grainman

    grainman Active Member

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    it appears when the amp is running no guitar plugged
    like i said v1 unplugged no noise
    thanks for helping me out guys i appreciate
     
  11. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    As @Neal mentioned above the likely suspects are the V1 plate resistors.

    Can you or do you feel comfortable taking voltage readings in a tube amplifier with a multimeter? Voltage readings will help. You can also chopstick around V1 especially at R7, R8, C3 and C4 to see if it causes noise/intermittence. (refer to schematic link)

    If not, bring it to a decent technician.

    Refer to this schematic. It should look like your amplifier if it has a Marshall installed effects loop.
    https://drtube.com/schematics/marshall/1959-01-60-02.pdf
     
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  12. 67Mopar

    67Mopar Well-Known Member

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    Could be a lot of things. In this order...
    1. Clean all input and output jacks + all tube sockets with Deoxit. Check...
    2. Closely check the tube sockets for damage. Check...
    3. Replace all tubes with a know viable set. Check...
    4. Remove tubes, and retouch all of the tube socket solder points with fresh tin/lead solder. Check...
    5. Check plate resistors.
    6. Check PT for a short between HT and B+ and ground.
    7. Measure DC on all filter caps.
    8. Lift one end of the bright cap from volume pot.

    I had this same issue with my RK1OO. I skipped cleaning the input jack, and after many hours of troubleshooting, it ended-up being a dirty input jack. The CLIFF jacks are notorious for getting dirty. I clean mine 3 times a year, just to be sure. As a matter of fact, my Silver Jube jacks need cleaning.
     
    Last edited: Aug 2, 2019
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  13. grainman

    grainman Active Member

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    thanks guys..i'll give it a try tommorow or later on this week ...with the schematics i should be able to locate things if someone has the voltages ..thanks for ur help /time
     
    Last edited: Aug 3, 2019
  14. ampmadscientist

    ampmadscientist Well-Known Member

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    Plate resistors can definitely add noise but:
    the majority of noise (HISS) comes from the 68K input jack resistors. This has been proven.

    To prove this, put a jumper across the 68K resistors, then repeat the tests.
    If the noise goes away when the 68K resistors are jumpered, then you know whats causing it.
    Also, you can just connect the tube side of the 68K resistors to ground, then re-test. (use a clip lead to ground the resistors on the tube side of the resistor)

    Plate resistors can get noisy also, but I suspect this is input noise from the 68K resistors.

    PS this noise is normal on all high gain amplifiers.
     
    Last edited: Aug 2, 2019
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  15. grainman

    grainman Active Member

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    ok guys i checked the 68k resistors at input they seem off ...the ones on the normal ch are both 33k and the bright ch one is 63 and the other 65 ... theres one think who bothers me , dont you think the amp will not making noise when im not plug in if theres trouble with them resistors? ..i cleaned the tube sockets and changed the tubes..and still the noise is there ...mmm i still have to check the plate resistors ..i forgot about em ..it might be the trouble...
     
  16. ampmadscientist

    ampmadscientist Well-Known Member

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    You cant measure the resistor until you plug into the jack (a cable with nothing else attached to the other end)..
    But that's not the point, the resistors are probably good. Noise (hiss) is normal for carbon resistors.

    There are lower noise resistors than carbon such as metal film and wire wound, bulk metal foil.
    As it turns out you can hit a -40 noise floor with bulk metal foil.

    [​IMG]
     
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  17. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Frying bacon is not a white noise sound. Proceed.
     
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  18. neikeel

    neikeel Well-Known Member

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    Problem with bulk metal foil is that most are surface mount and will be tricky to fit to your Marshall.
    You can however get 2w Metal Film resistors that are identical in size and shape to the commonly available Vishay 1 watt used in most turret board builds ( ie same size as old 0.5w Piher and Iskra Carbon films and the 0.5w AB carbon comps).
    The snap crackle and pop/frying bacon noise is often v1 plate resistors getting noisy - Marshall rarely used carbon comps there (unlike Fender). I’m surprised a noise gate abolished this.
    The OP describes more like front end hiss which of course is the best reason to justify a noise gate in a high gain amp, imo.
     
    Last edited: Aug 11, 2019
  19. ampmadscientist

    ampmadscientist Well-Known Member

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    The plate resistors can get noisy and make a frying bacon noise. (also)
     
  20. grainman

    grainman Active Member

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    yep a gate in the efx loop kills the bacon noise...but im getting fed up of the gate effect...
     

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